Body temperature during and following 10-day subcutaneous infusion of clonidine in the rat.

Body temperature in the rat was measured during and after cessation of the continuous subcutaneous infusion of clonidine (10 micrograms/kg per hr) for 10 days. The body temperature of control animals displayed a distinct circadian rhythm. On each day the mean body temperature over the dark phase (2000-0800 hr) was consistently higher (0.6-0.9 degrees C) than the following light phase. The infusion of clonidine was essentially devoid of initial effects on body temperature. However, during the light phases of day 2 onwards the mean body temperature of the animals treated with clonidine was consistently higher (0.4-0.6 degrees C) than that of controls. No such differences were observed during the dark phases. It appeared that the infusion of clonidine limited the fall in body temperature which normally occurred at the onset of the light phases and this resulted in the treated rats displaying a relative hyperthermia. On cessation of the infusion of clonidine (at 2400 hr on day 11) a distinct hyperthermia was observed within 2 hr and was sustained for the remainder of the dark phase and subsequent light phase. This post-infusion hyperthermia was more pronounced than that observed during the period of infusion of clonidine. These results demonstrate that the circadian control of body temperature is disturbed both during and after continuous infusion of clonidine.

Age-related changes in neuropeptide Y immunoreactivity (NPY-ir) in the cortex and spinal cord of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats.

The concentrations of neuropeptide Y immunoreactivity (NPY-ir) were measured in the cortex and cervical, thoracic and lumbar spinal cord of 8-, 18- and 31-week-old normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). This peptide was measured using a highly sensitive and specific radio-immunoassay (RIA) developed in our laboratory. The concentrations of NPY-ir in the cortex, cervical and thoracic spinal cord were significantly different between the two strains, with the levels being consistently lower in the SHR strain independent of age. While there was no obvious change in the levels of NPY-ir in the cortex with increasing age, there was a general trend for the levels to fall in all three spinal cord regions. The rate of decrease of NPY-ir in the thoracic spinal cord appeared greater in the SHR compared with the WKY rats. These biochemical differences observed in the cortex and thoracic spinal cord of SHR and WKY rats may be related to the behavioural and blood pressure differences observed in these strains.

The concentration of neuropeptide Y immunoreactivity falls with age selectively in microdissected regions of the ventrolateral medulla of spontaneously hypertensive and normotensive Wistar-Kyoto rats.

The concentrations of neuropeptide Y immunoreactivity were measured in microdissected regions enriched in noradrenergic (A1, A2, A6) and adrenergic (C1, C2, C3) nuclei of the brainstem, and in the nucleus of the spinal tract of the trigeminal nerve (Sp5C) of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats at 8, 18 and 31 weeks of age. The aim of this study was to compare the manner in which changes in neuropeptide Y immunoreactivity levels related to increases in blood pressure with ageing in each rat strain. The concentration of neuropeptide Y immunoreactivity in the A1 nucleus progressively fell with increasing age in both SHR and WKY. In contrast, the levels of neuropeptide Y immunoreactivity in the C1 region fell at 18 weeks of age but did not fall further by 31 weeks. No significant age-related changes occurred in the concentrations of neuropeptide Y immunoreactivity in the A2, C2, A6 and Sp5C nucleus. The levels of neuropeptide Y immunoreactivity in the C3 region were below assay sensitivity. The neurochemical changes that occur in the A1 nucleus are consistent with the increase in blood pressure observed with ageing in both rat strains. However, this observation alone does not account for the elevated blood pressure measured in the SHR strain.

Comparison of ?-endorphin immunoreactivity in hypothalamic and brainstem nuclei of normotensive and age-matched hypertensive rat strains.

The concentration of ?-endorphin immunoreactivity was determined in 21 hypothalamic and brainstem nuclei of Sprague-Dawley (SD) and 6 and 14 week Wistar-Kyoto (WKY) and Spontaneously Hypertensive (SH) rats. The concentrations of ?-endorphin immunoreactivity were greater in the hypothalamic nuclei than in the brainstem nuclei approximately by a factor of 5. A significant strain-age interaction was observed in the ?-endorphin immunoreactivity levels in the anterior hypothalamic area, paragigantocellular reticular nucleus and locus coeruleus of age-matched SH and WKY rats in that immunoreactivity levels fell in the age period studied (6-14 weeks) in WKY rats and rose in SH rats. These biochemical differences are related in time to a growth period during which there are large increases in blood pressure in the SH rat and may thus have a pathogenetic significance.

Differences in regional brain concentrations of neuropeptide Y in spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats.

Regional brain concentrations of neuropeptide Y immunoreactivity (NPY) were measured in age-matched Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats using a sensitive and specific radioimmunoassay developed within our laboratory. In 5 of the 9 brain regions examined the SH rats had significantly lower NPY levels compared to the WKY strain. The largest differences occurred within the cortex (-43%), and cervical (-30%) and thoracic spinal cord (-30%), whilst smaller differences were observed in the midbrain (-11%) and medulla oblongata-pons (-18%). The concentrations of NPY in the hypothalamus and hippocampus did not vary between the strains. The SH rats contained significantly greater (+18%) NPY levels in the striatum compared to the WKY rats.

Modification of the circadian body temperature rhythm of the spontaneously hypertensive rat during and following cessation of continuous clonidine infusion.

The effects of continuous clonidine infusion (10 micrograms/kg/h for 10 days) and the cessation of this infusion on the circadian body temperature rhythm of the spontaneously hypertensive (SH) rat were examined. This circadian rhythm was blunted significantly during the infusion of clonidine. The fall in body temperature which normally occurs at the onset of each light phase was attenuated during the clonidine infusion, and as such, these rats displayed a relative hyperthermia over the light but not the dark phases. On cessation of infusion (24:00 h), a distinct hyperthermia occurred within the immediate dark phase and the subsequent light phase. The results demonstrate that the circadian control of body temperature is disturbed both during and after continuous clonidine infusion.

Comparison of neuropeptide Y immunoreactivity in hypothalamic and brainstem nuclei of young and mature spontaneously hypertensive and normotensive Wistar-Kyoto rats.

The concentration of neuropeptide Y immunoreactivity (NPY-ir) was measured in 8 hypothalamic and 5 brainstem nuclei of 6- and 14-week-old spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats. Strain differences were observed in 3 hypothalamic nuclei and age-dependent changes occurred in 3 hypothalamic and 2 brainstem nuclei. In both the ventromedial hypothalamic nucleus and locus coeruleus the observed change in NPY-ir with age in SH rats was significantly different to the change observed in the WKY. These strain- and age-related differences in NPY-ir may be of relevance in the development of hypertension in the SH rat.

Distribution of neuropeptide Y immunoreactivity in the rat basal ganglia: effects of excitotoxin lesions to caudate-putamen.

The distribution of neuropeptide Y-like immunoreactivity (NPY-LI) within the rat basal ganglia was studied using microdissection with a sensitive radioimmunoassay, and excitotoxin lesions were made in an attempt to characterise the neurones containing NPY in this brain area. Immunoreactivity was unevenly distributed in the basal ganglia of control rats, with concentrations in the caudate-putamen (CP) and nucleus accumbens being appreciably higher than those found in the globus pallidus and substantia nigra (SN). Within the CP, immunoreactivity was concentrated in caudal and extreme rostral aspects. N-Methyl-D-aspartate lesions of the rostral CP significantly reduced immunoreactivity in this area, whilst levels in other regions of the basal ganglia were unaffected. Neurones containing NPY-LI are likely to be intrinsic to the CP and do not appear to project to the globus pallidus or SN.

Intrathecal kynurenate reduces arterial pressure, heart rate and baroreceptor-heart rate reflex in conscious rats.

In the present study, an excitatory amino acid (EAA) pathway in the spinal cord which maintains sympathetic vasomotor tone in conscious rats has been investigated. To this end, the cardiovascular effects of an intrathecally administered EAA antagonist, kynurenate (KYN), were studied in conscious rats. KYN (0.5 mumol in 10 microliters) caused a dramatic reduction in mean arterial pressure (MAP) and heart rate (HR) that persisted for 2-3 h, and also resulted in extensor paralysis of the hindlimbs. The time courses of fall in MAP and HR and hindlimb paralysis were similar. Baroreceptor-HR reflex activity was also markedly impaired after KYN, suggesting functional diminution of sympathetic outflow at the level of the spinal cord after blockade of EAA receptors by KYN. Xanthurenate, a metabolite of KYN without EAA antagonistic properties, produced negligible effects at the same dose of KYN. While these findings do not identify the putative EAA pathway, they do provide the first demonstration that this system is tonically active in conscious rats.

Comparison of a once-a-day sustained-release morphine formulation with standard oral morphine treatment for cancer pain.

Kadian/Kapanol (K) is a capsule formulation of morphine designed for 12- or 24-hourly dosing. This double-blind study compared the efficacy and safety of K every 24 hr to K every 12 hr and MS Contin tablets (MSC) every 12 hr. One hundred fifty-two patients with cancer pain were titrated to adequate analgesia with immediate-release morphine (IRM) solution. Stabilized patients were randonized to one of the three treatments for 7 +/- 1 days. Rescue medication was IRM tablets. Efficacy and safety were assessed by time to first remedication and total dose of rescue medication, pain scores, global assessments, and incidence of morphine-related side effects. Fifty-four patients were treated with K every 24 hr. 45 with K every 12 hr. and 53 with MSC every 12 hr. Mean age was 61 years and mean total daily dose of morphine was 138 mg. Forty-six percent of the K every 24 hr patients, 51% of the K every 12 hr patients, and 55% of the MSC every 12 hr patients required rescue medication on the final day. Time to remedication was 16.0 hr for K every 24 hr, 9.1 hr for K every 12 hr and 8.7 hr for MSC every 12 hr (P = 0.0010). Patient global assessment significantly favored K every 24 hr over MSC every 12 hr (P = 0.018). There were no statistically significant differences among the treatments for any morphine-related side effects when adjusted for baseline. K had efficacy and safety profiles similar to MSC every 12 hr but had the advantage of 12- or 24-hourly administration.

Surgical and pharmacological reductions in sympathetic nerve activity increase the neuropeptide Y-immunoreactivity content of the rat iris but not the vas deferens.

Decentralization of the superior cervical ganglion (S.C.G.) of the rat elevated the neuropeptide-Y immunoreactivity (NPY-ir) content of the ganglion on day 1 (+43%) but not on day 3 post-surgery. The content of NPY-ir in the iris was increased by decentralization (+40%) 3 days post-surgery, and treatment with clonidine (+43%), and pempidine (+82%). The levels of NPY-ir in the rat vas deferens were not affected by either surgical or pharmacological treatment. These results suggest NPY is released from sympathetic nerves in the iris but not vas deferens during normal sympathetic activity.

The development of a relative hyperthermia during continuous clonidine infusion in the rat.

In rats the continuous infusion of clonidine (10 micrograms kg-1 h-1) produces a relative hyperthermia of approximately 0.6 degree C during the light phases but not the dark phases of a 10 day infusion period. It appears that the relative hyperthermia results from a clonidine infusion-induced attenuation of the fall in body temperature which normally occurs at the onset of the light phases.

Differential effects of surgical sympathectomy on rat heart concentrations of neuropeptide Y-immunoreactivity and noradrenaline.

The aim of this study was to estimate the proportion of cardiac neuropeptide Y-immunoreactivity (NPY-ir) which is not present in sympathetic neurones innervating the rat heart. The procedure employed was to surgically sympathectomize the heart and then measure the remaining cardiac concentrations of NPY-ir and noradrenaline (NA). Unilateral (left) sympathectomy significantly reduced the levels of NPY-ir and NA in all regions of the heart (by 40-70%) except for the NPY-ir in the right atrium which was unaltered. The effect of bilateral sympathectomy was significantly greater than that of unilateral sympathectomy. Unilateral and bilateral sympathectomy produced similar reductions in the concentrations of NPY-ir and NA in the ventricular tissue. In contrast dissimilar changes were produced in the atrium. Although bilateral sympathectomy almost totally depleted the NA from the right atrium (by 98%), the NPY-ir levels were only reduced by 50%. These results indicate that approximately half the content of NPY in the right atrium is not present in sympathetic noradrenergic neurones. This pool may occur in the previously described intrinsic neurones of the right atrium.

Comparison of the Arrhythmogenic Actions of (-)-Isoprenaline, Dobutamine and the selective beta 1-adrenoceptor agonist, (+/-)-(1-[3',4'-dihydroxyphenoxy] -2-hydroxy-[3",4"-dimethoxy phenethylamino]-propane)-oxalate (Ro 363).

In guinea-pig left atrial preparations, concentrations of (-)-isoprenaline and (+/-)-(1-[3',4'-dihydroxyphenoxy] -2-hydroxy-[3",4"-dimethoxyphenethylamino]-propane)-oxalate (Ro 363) causing maximal inotropic responses produced small reductions in effective refractory period. Dobutamine had little effect on the refractory period except at supramaximal inotropic concentrations, when increases in effective refractory period were produced. Isolated perfused heart preparations from guinea-pigs developed arrhythmic contractions following the administration of (-)-isoprenaline, Ro 363 and dobutamine in doses producing 70-100% of their maximal chronotropic responses. The arrhythmogenic activity of the three agonists paralleled their respective beta 1-receptor stimulant properties. In chloralose-anaesthetized cats, the 3 agonists, (-)-isoprenaline, Ro 363 and dobutamine, when compared to epinephrine (adrenaline), were essentially devoid of arrhythmogenic activity in animals in which cardiac sensitization was induced by 3-dimethylamino-2-methyl-2-phenoxypropiophenone hydrochloride (U-0882) or halothane. However, all 3 agonists elicited ventricular arrhythmias following the administration of subarrhythmic doses of ouabain and increased the number of subauricular escape beats which occurred during vagal nerve stimulation in non-ouabain treated animals. In all cases the arrhythmogenic activity of the drugs paralleled their relative activity for eliciting rises in heart rate.

Beta-adrenoceptor selectivity of dobutamine: in vivo and in vitro studies.

We compared the beta-adrenoceptor stimulant actions of dobutamine and (-)-isoprenaline in isolated tissue preparations (atria, trachea, and uterus) from the guinea pig and in chloralose-anaesthetized, vagotomized cats (arterial blood pressure, heart rate, hindlimb perfusion pressure, and soleus muscle contractility). The results obtained in these experiments indicate that, on a dose basis, dobutamine shows little selectivity in producing alpha-, beta 1-, and beta 2-adrenoceptor-mediated effects. In phentolamine-treated cats, reductions in arterial pressure and total peripheral resistance produced by infusions of dobutamine were little affected by the beta 2-adrenoceptor-selective antagonist butoxamine, but were antagonized by atenolol. The rise in cardiac output produced by dobutamine involved increases in both heart rate and stroke volume. There was little indication of a selective inotropic action, a feature that confirmed the results obtained in isolated atrial preparations. The increase in cardiac output appeared to involve both alpha- and beta-receptor-mediated actions, because phentolamine reduced the rise in cardiac output by reducing stroke volume.

Leakage of catecholamines from rabbit cerebrospinal fluid following intracerebroventricular injection.

The intracerebroventricular (i.c.v.) injection of (-)-isoprenaline and the selective beta 1-adrenoceptor agonist, RO363, elicited reproducible dose-related increases in heart rate in unanaesthetized and anaesthetized rabbits. (-)-Isoprenaline produced vasodepressor effects in unanaesthetized animals, whereas both catecholamines decreased blood pressure in anaesthetized rabbits. Pretreatment with guanethidine sulphate (5 mg/kg i.v.) reduced but did not abolish the tachycardia elicited by i.c.v. RO363, whereas heart rate responses to i.c.v. (-)-isoprenaline were unaffected. Pretreatment of anaesthetized rabbits with hexamethonium bromide (10 mg/kg i.v.) did not markedly affect the tachycardia elicited by i.c.v. RO363 and reduced the response to i.c.v. (-)-isoprenaline in only one out of five experiments. The results suggest that there is a marked leakage of centrally administered catecholamines into the peripheral circulation and that the rabbit may be unsuited for examining centrally mediated cardiovascular effects of catecholamines.

Altered levels of neuropeptides in the medulla and spinal cord of spontaneously hypertensive rats.

1. Spontaneously hypertensive rats (SHR) are useful for investigating the possible pathophysiological and neurochemical basis of human essential hypertension. 2. The accepted pathogenic mechanism of hypertension in SHR is an increased central sympathetic drive which results in an increased peripheral resistance. 3. The neurochemical basis of the increased sympathetic drive is unknown. The observation that there are reduced levels of neuropeptides (vasoactive intestinal peptide, neuropeptide Y, cholecystokinin octapeptide, neurotensin and calcitonin gene related peptide) in the spinal cord in SHR rats compared with age and gender matched Wistar-Kyoto normotensive rats could provide a basis for understanding the mechanism of hypertension in SHR.

Right ventricular neuropeptide Y levels in a rat model of left ventricular failure.

Neuropeptide (NPY) and norepinephrine (NE) concentrations were measured in the right ventricle (RV) of rats with cardiac failure resulting from coronary artery ligation. RV NE concentrations fell significantly in rats with infarcts while RV NPY concentrations were unaltered.